The present invention relates to a device for clamping a work piece on a chuck, this device making it possible, during clamping, to hold the piece axially so that it bears against stops serving to pre-position the piece and disposed on the chuck.
Some known chucks are equipped with jaws capable of moving, in relation to the axis of the chuck, radially, but not axially. There are also known devices permitting combined radial and axial movement on the part of each jaw, so as to be able simultaneously to clamp a piece and to press it against the chuck. However, conventional chucks do not enable the radial movement of the jaw to be decoupled from its axial movement.
To effect optimum clamping, i.e. clamping the members for which are capable of holding a work piece firmly, but without being liable to damage the surface of said piece, arrangements are usually made (insofar as the profile of the piece permits) to cause the jaws to cooperate with certain suitable parts of the piece, such as grooves, recesses, shoulders or projections.
Now, the dimensions of the blanks inevitably differ to a certain extent from the design profile. In order to position the jaws on the piece so as to be able to effect optimum clamping, one then has to adjust its position in space, hence in relation to the chuck. Generally speaking, this adjustment is not confined to a simple radial translation. As a result, it is not possible to preposition a piece on a conventional chuck (by causing it to bear on reference stop means disposed for this purpose on the face of the chuck), and then, without axially displacing it, accurately mate with the profile of the piece at the time of clamping.
This is unfortunate, as industry has a real need for a chuck having this capability. This need arises, for example, when it is wished to clamp a blank on a chuck in a quite particular position which will make it possible to machine the piece so that it will run as true as possible.
The present invention solves this problem by allowing the jaws to move radially, axially, and even transversely, with a certain measure of mutual independence.
The chuck according to the invention includes a plurality of jaws, each of which is fixed to the forward end of a jaw carrier arm, said arm being borne by a pivot joint mounted on the body of the chuck and the rotation of which imparts to the jaw an essentially radial movement, said rotation being controlled by radially displacing a sliding member pushing a truncated sphere housed between said sliding member and a recess provided in the arm to the rear of said pivot joint. Furthermore, said truncated sphere is capable of sliding over the plane surface of contact with the sliding member, said jaw carrier arm then sliding in the pivot joint in an essentially axial direction, while being drawn rearwards by a return spring.
According to other, additional features, the rear portion of the jaw carrier arm moves inside a recess provided in the plate on which the chuck is mounted and the width of which is slightly greater than that of said arm, so as to confer on the arm a certain latitude of movement in the transverse direction.
Thus, the jaws can each come into contact with the work piece and adapt to its exact profile by subjecting it only to a radial translation, before proceeding to its final clamping.